1. Field of the Invention
The present invention relates to a transmission apparatus including a hydro-mechanical stepless transmission (hereinafter, “HMT”), which is a combination of a hydrostatic stepless transmission (hereinafter, “HST”) and a planetary gear assembly, applied for a working vehicle such as a cart.
2. Related Art
Conventionally, as disclosed in Japanese Unpatented Application Publication No. 2002-67719, there is a well-known cart having a belt type continuously variable transmission (CVT) serving as a main speed changing unit, combined with a mechanical gear transmission on the downstream thereof serving as an auxiliary speed-changing unit, wherein a mechanical reverser for changing the forward and backward travel direction of the cart is disposed in the auxiliary speed-changing unit.
The belt type CVT has the disadvantageous of insufficient power transmission efficiency, because of frictional pressure of a belt against a pulley, and because of slipping of the belt against the pulley when the belt is wet.
The auxiliary speed-changing gear transmission having the mechanical reverser requires a clutch. In other words, the clutch must be disengaged so as to cut off power transmission for changing the reverser, thereby causing a shock and noise of meshing gears. A hydraulic clutch can reduce such shock and noise; however, it requires an expensive hydraulic fluid source. Further, the hydraulic clutch also has to cut off power transmission for changing the forward and backward traveling direction of a cart, thereby still causing a shock.
Another problem of the cart is that a cargo deck is reduced in volume by the gear transmission disposed therebelow. From this viewpoint, a compact transmission to be disposed below a cargo deck of a cart is requested. Such a compact transmission can increase the volume of the cargo deck, reduce the height of the cargo deck for convenience of loading, increase a road clearance below the cart, and stably lower the gravity center of the cart.